U.S. Pat. No. 5,440,353 is incorporated by reference to show a horizontal moire cancellation circuit which is useful in the invention described below.
1. Field of the Invention
The invention relates generally to cathode-ray tube displays and particularly to raster scanned displays, especially color displays. More particularly, it relates to automatically correcting such displays to eliminate or at least substantially reduce horizontal moire interference.
2. Background
Moire effects create ripple effects in video displays which smear detail and detract from the picture quality. Corrections may be applied to the video signals to suppress moire effects. To correct for horizontal moire, the lines of the display are slightly delayed. In the prior art, correction of horizontal moire are manually activated and the correction is applied to the entire screen. When only a section of the display requires correction, applying the correction to the entire screen degrades resolution of the displayed image and defocuses all or part of the display.
In accordance with the invention, the existence of a moire pattern on a display is determined automatically. A count of the number of pixels occurring in horizontal lines of a scanned CRT display is made and compared to a reference count. If the counts are substantially equal, a moire correction circuit is enabled for that section of the display. Sections of each horizontal line can be separately checked for the presence of a moire pattern. The moire correction circuit is automatically disabled for sections of the display for which it is not required.